To enhance performance of wireless communication systems, beamforming is often applied. In general, beamforming increases signal reception sensitivity of a particular receiver by giving directionality to the beam using multiple antennas. The beamforming may be categorized according to transmission beamforming and reception beamforming based on which communication element conducts the beamforming operation.
FIG. 1 depicts beams of a base station applying a beamforming operation in a wireless communication system. Referring to FIG. 1, the base station covers a plurality of sectors and forms a plurality of beams having directionality in each sector. When the beamforming is applied, the propagation pattern narrows. Hence, it is necessary to use more beams than antennas in the sector in order to service one base station cell or sector. Because of the narrow beamforming of the base station, a user station can obtain better channel state.
The user station needs to select the best beam from the multiple beams of the base station and select a new beam according to its rotation or movement. As the beam becomes narrower, the beam is selected more on a more frequent basis. When the user station applies beamforming, the best channel state is attained only when the beam direction of the base station matches the beam direction of the user station. However, unlike the stationary base station, the user station is mobile. Moreover, the direction of the station facing the base station can easily change. As a result, the beam directions of the user station and the base station can be misaligned frequently.